It’s worth noting their last clue was ‘firewall’, and not ‘wall’. This was likely to keep them away from ROCK, SKYSCRAPER, and possibly FIELD.
With ‘Construction’, I think we open SKYSCRAPER. From there, I think we need to look slightly creatively at possible options, given the best options are both gone already, and are Blue anyways.
Cap - Hard Hats are commonly required in Construction.
Pipe - Plumbing, Gas, Electricity - all things in various Construction industries that would use pipe.
Shoe - Steel Toe Boots are often worn on Construction sites.
Field - A place Construction might take place.
I could stretch to Stick, but I think there are better options. I think we should avoid Rock.
We have 4 words, and we need 9 total. We have 4 for ‘Construction’, and 1 unguessed for ‘Tomato’. If those don’t overlap then we’re clued to win. I’m not convinced it’s that easy though. While they only need 3 to win, I think it’s safer for us to assume FIELD is a double word for us - meaning both ‘Construction’ and ‘Tomato’.
I think our strongest 4 are: Skyscraper, Field, Cap & Pipe.